extcon: ptn5150: Simplify getting vbus-gpios with flags

Instead of obtaining GPIO as input and configuring it right after to
output-low, just use proper GPIOD_OUT_LOW flag.  Code is smaller and
simpler.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Vijai Kumar K <vijaikumar.kanagarajan@gmail.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>